I initially thought there should be a way to bolt on a small aftermarket turbo onto my naturally-aspirated Honda D17A2 (9.9:1 compression ratio) engine in my EM2 Civic EX without having to switch from running Regular unleaded fuel (86-89 AKI) to Midgrade (88-91 AKI) or Premium (91+ AKI) if I don't desire the maximum horsepower potential, but a modest horsepower gain (say +38 hp) in the lower-mid-range powerband and for better overall engine efficiency. However, a previous question (by Annath) and answer (by Bob Cross) that I stumbled across on this site seems to have me questioning this initial upgrade thought.
Now it was my understanding that there are numerous factors that can affect the maximum allowable effective compression ratio in relation to the fuel (octane rating) and since it's best to have an effective compression ratio set as high as feasible without encountering detonation at the maximum load condition, I began to think that the D17A2's 9.9:1 compression ratio might not be the immediate drawback most would think it to be in regards to forced induction and the 87 AKI fuel. The factors that I'm aware of that influence the compression ratio include: fuel anti-knock properties (fuel octane rating), boost pressure (psi), intake air temperature, combustion chamber design, ignition timing, valve events, and exhaust backpressure. So if you can lessen or modify one or more of the other factors in an attempt to balance the increase from chamber pressure, then perhaps a safe offset will occur.
Thanks to many modern normally-aspirated engines having well-designed combustion chambers and ECUs (or PCMs) providing appropriate self-tuning, I thought my D17A2 engine could handle a modest amount of boost with no significant change to its compression ratio. Am I wrong in thinking this? By making sure that the turbo I installed was small, wasn't set above say... 5 psi at max, had an intercooler installed for decreasing the intake air temperature, I believed my car's ECU could enrich the fuel/air mixture so that it would run even cooler yet, plus modify the ignition timing all in order to prevent premature detonation and provide a modest horsepower gain. Plus, thanks to the size of the turbo the power gain would affect the power band between 2000 - 4000 rpms, where most of my daily driving takes place. On top of that I thought I might even see a slight increase to the vehicle's fuel efficiency as the engine's cylinder's volumetric efficiency increased thanks to the forced induction. Am I overlooking something or is this a practical outlook to the potential of adding a turbo to my vehicle while maintaining the use of 87 AKI octane fuel? Do you think my Civic's ECU could handle the changes that would come with installing a turbo as I described or would I need to have the ECU flashed and re-tuned... my fear is this would be a potentially disastrous step unless under taken by a true specialist who understood the installed turbo and the D17A2 engine. I worry that this would mean that it would be very expensive, too expensive, to get the tuning just right, but maybe the default ECU setting would be sufficient. Anyways, what's your thoughts and is there a way to mathematically determine whether these aspirations of mine are even feasible?